Method for automatic control of a microwave oven

Abstract: This invention relates to a method for automatic control of a microwave oven, which can make precise cooking control available by classifying the control of cooking into a case when cooking is completed below the boiling point of water such as thawing and warming up and a case when cooking is completed above the boiling point of water. To achieve this, this invention sets the cooking time period by setting the time when the output voltage of a temperature detection sensor reaches to a rise starting point as a reference detection point if cooking courses of thawing or warming up are selected upon identification of selection of cooking course of cooking courses with no water boiling like thawing or warming up and general cooking courses accompanying water boiling, and by setting the time when the output voltage of the temperature detection sensor reaches to the maximum as a reference detection point if general cooking courses accompanying water boiling are selected.

Description: FIELD OF THE INVENTION This invention relates to a method for automatic control of a microwave oven, more particularly to a method for automatic control of a microwave oven, which can make precise cooking control available by classifying the control of cooking into a case when cooking is completed below the boiling point of water such as thawing and warming up and a case when cooking is completed above the boiling point of water. BACKGROUND OF THE INVENTION Technology for automatic cooking with a microwave oven has been developed more in view of simplification of cooking for enhancing the convenience of consumers. Various sensors have been used in a currently marketed microwave oven having automatic cooking function, and according to this, the microwave oven has been closed up as a large field of sensor market. The sensors employed in the microwave oven up to now are sensors in the heating chamber for detecting the temperature, sensors for detecting humidity, sensors for detecting gases generated at cooking, vapor detection sensors, sensors for detecting weight of the food and sensors for detecting weight of the food, and there are many methods for controlling cooking using the sensor signals out of those sensors (see e.g. US-A-4 376 131 and US-A-5 155 339). However, even though those sensors are applied to cooking in many ways, still it is not enough to applications for the cases of cooking with weak heat. That is, in case of warming up of food, or thawing meat or fish, though the point of control should be decided based on the quantity of moist generated throughout entire cooking period, i.e., based on humidity, since it is hard to detect the humidity at warming up or thawing, there is problem of difficulty in controlling of cooking. Further, in case a user intends to carry out thawing in a same container successively, there is problem of malfunction due to miscalculation of control time caused by increase of sensed humidity come from the vapor generated in the water left from the previous cooking, i.e., from the previous thawing which boils first. As a counter measure for this, even though solutions, such as explaining the necessity of additional container cleaning in case of thawing and trying it known to all users through the users' manual, are employed, it is not desirable because it is highly possible to make the users feel cumbersome and inconvenient. There are many control algorithms employing the foregoing sensors, of which cooking period control algorithm is typical one that is used in applications of humidity sensors and gas sensors. Typical manner of change of the detected sensor output voltage during cooking period when gas sensors or humidity sensors are employed in a general microwave oven exhibits, as shown in FIG.1, sharp increase of output of the sensors at starting of boiling of water due to generation of vapor or gas as cooking of food proceeds. Total heat Q can be expressed in following equation, where the Q is the total heat until food in a microwave is heated and cooked to an appropriate state. Q = M x C x ( tf - ti ) + ( M x B ), where, C is specific heat of the food, M is quantity of the food, tf is boiling temperature of moist in the food, ti is initial temperature of the food, and B is heat proper to latent heat and degradation of food. And since the total heat Q will be the same with the total heat generated by the microwave oven, the total heat can be expressed as follows; Q = T x P where, T is total time period of cooking, and P is output of the microwave oven. Therefore, the following equation (3) can be obtained from equations (1) and (2). T = 1/P(MxCx(tf - ti)) + 1/P(M x B) Since the first term is the period from the starting of cooking to the boiling of moist in the food, and the second term is the period from the starting of vaporization of the moist to completion, the total period of cooking T can be expressed as follows; T = T1 + KT1 wherein, T1 = 1/P ( M x C x ( tf - ti)), K = B/(C x ( tf - ti )), where the K is a cooking constant. Thus, if an appropriate cooking constant K is applied, depending on the kind of cooking, an automatic cooking can be carried out upon application of keys arranged on the key board of the microwave oven. That is, if reference detection point is set based on the time when the food starts to boil that is a point when the output signal of a sensor rises sharply, the reference detection period that is a time period from start of cooking to the detection will be T1. Accordingly, the microwave oven will be operated additionally as much as the time period obtained by multiplying the time period T1 determined as such to the cooking constant K. That is, the total operation time period of the microwave oven will be a period the time period corresponding to the reference detectionperiod T1 is added to the time period the determined reference detection period T1 and the cooking constant K is multiplied. However, microwave ovens, controlling in general cooking completion point with currently used humidity sensors, temperature sensors and gas sensors, the weight given to thawing function in microwave oven functions is increasing day by day as cooking of frozen food become frequent in modern life pattern. Meantime, in case the cooking should be finished below boiling point of water as in such cases of warming up or thawing, the microwave oven has had problem in that it should be provided with supplementary sensors, for example weight sensors, because an algorithm that should employ boiling point of water as a reference detection point used in general microwave oven can not be applied thereto. SUMMARY OF THE INVENTION The object of this invention is to provide a method for automatic control of a microwave oven, which can make a precise cooking control available that allows setting of reference detection point even below boiling point of water using a sensor that can detect radiation heat generated during cooking of food without any addition of supplementary sensors. These and other objects and features of this invention can be achieved by providing a method for automatic control of a microwave oven as defined in claim 1. BRIEF DESCRIPTION OF THE DRAWINGS FIG.1 is a wave pattern of output voltage of a sensor detected at cooking of a general microwave oven. FIG.2 is a perspective view of a microwave oven this invention applied thereto. FIG.3 is a wave pattern of output voltage of a sensor detected at cooking frozen meat for a microwave oven in accordance with this invention. FIG.4 is a flow chart of a method for automatic control of a microwave oven in accordance with this invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIG.2, a microwave oven having the method for automatic cooking control applied thereto includes a door 6 for open/closing and a control panel 2 for operation and display positioned at front of a heating chamber 1, a rotating shaft 5 connected to a turntable driving motor positioned in the heating chamber 1, a tray 4 and rollers 7 for rotation positioned on top of the rotating shaft 5, and, though has not been shown herein, a magnetron of a heating source and a high voltage transformer positioned outside of the heating chamber 1. Positioned in the heating chamber, though it has not been shown herein, is a sensor for remote sensing of food by detecting radiation heat emitted from the food, wrap enclosing the food or a container. The sensor used herein is a thermopile, or a bolometer type thermistor that utilizes the radiation heat absorption properties of a black body and a non-black body. FIG.3 show an example of detection with a thermopile used in this invention at cooking, showing output voltage of a sensor at cooking of 200g frozen meat for 20 minutes. Variation of output voltage of a sensor as the cooking proceeds is to be explained hereinafter, referring to FIG.3. First, when a piece of frozen food at a temperature below 0 deg.C has been put into the microwave oven, output voltage of the sensor drops sharply. Such a phenomenon can be utilized as an automatic thawing recognition function. Once the magnetron is put into operation, at first a water film is formed on the surface causing the surface temperature rise much faster than the interior showing rise of output voltage of the sensor. Therefore, at actual thawing, heating of the interior of the food under cooking by the heat transfer of the food itself should be carried out in parallel with the heating by the magnetron through operating the magnetron continually. As can be seen from FIG.3, thawing is completed when the output voltage of the sensor comes back to a range of value before the food was put in. Accordingly, an absolute value A obtained through experiments can be selected as a reference point, i.e., as a thaw reference point for determining the time of cooking completion. The thaw reference point A is corresponds to about the surface temperature 5 deg.C and corresponds to the output voltage of about 1.67 V of the temperature detection sensor. On the other hand, when water starts to boil by continuous heating, the signal output exhibits a rapid rise due to rapid generation of vapor, which point is set as a reference sensing point, i.e., the maximum rise point B of the cooking course having water boiling. Of such variation of output voltage of the sensor, kind of thawing being determined between the thaw reference point A and the maximum rise point B, in case of thawing and warming up, actual cooking time period can be controlled properly by detecting the thaw reference point A. That is, automatic cooking can be made available through, in case of thawing, obtaining the thawing completion time period by multiplying the output voltage of the sensor at the thaw reference point A having set as a reference detection point and applied thereto to the thawing cooking constant, and, also in case of warming up, obtaining the warming up completion time period, like the case of thawing after fixing the cooking constant, by multiplying the warming up cooking constant to the output voltage of the sensor at the thaw reference point A applied thereto. And in case of cooking requiring a full boiling of water, it is practicable to make the automatic cooking available with setting the reference detection point at the maximum rise point B and determining the required cooking constant. Accordingly, when a user applies a cooking selection key depending on the kind of cooking using the output voltage of the sensor, the reference detection point can be set at the thaw reference point A or at the maximum rise point B as shown in FIG.3. That is, in case of thawing, the thaw reference point A is set as the reference detectionpoint, and in case of general cooking accompanying water boiling, the maximum rise point is set as the reference detection point. Once the reference detection point has been set through the foregoing process, the time period T1 required for reaching to the reference detection point from the starting of cooking can be applied, and thereafter a method similar to the control method used in the conventional art can be utilized. That is, since the total cooking time period T is, T = T1 + KT1, if the microwave oven is operated additionally for the time period obtained by multiplying the already tabled and stored cooking constant K to the reference detection period T1, the cooking can be completed. A method for automatic cooking control in accordance with this invention using output voltage of a sensor is to be explained hereinafter, referring to FIG.4. First, a cooking constant storing step 10 for making a table and storing the table of cooking constants K depending on the kinds of cooking, for example warming up, thawing, scalding, smothering is carried out. After the cooking constant storing step has been carried out, a microwave oven initializing step 11 for searching any application of menu key, initializing a cooking time period monitoring timer for measuring cooking time period when menu key has been applied 12, rotating a turntable instep 13, storing an initial value of the temperature detection sensor instep 14, and setting corresponding cooking constant instep 15 is carried out. Herein, the cooking constant K is set by the menu key application. That is, if the applied menu key is for warming up, a cooking constant corresponding to warming up is set, if the applied menu key is for thawing, a cooking constant corresponding to thawing is set, and if the applied menu key is for scalding, a cooking constant corresponding to scalding is set. After the microwave oven initializing step is carried out, a magnetron operation step 16 for operating a magnetron and actuating a cooking time period monitoring timer is carried out. After the magnetron operation step is carried out, a cooking course identification step 17 for identifying the menu key applied by a user at the initializing step of the microwave oven being a cooking course without water boiling is carried out. An additional magnetron operation time period setting step 18, 19, 20, 21, and 22 for the cooking course without water boiling is carried out for setting additional operation time period of the magnetron based on the time period the output voltage of the temperature detection sensor reaches to the thaw reference point at taking the thaw reference point A of the output voltage of the temperature detection sensor as the reference detection point and the set cooking constant when the applied menu key is for a cooking course without water boiling, for example for warming up or thawing as the result of carrying out of the cooking course identifying step. That is, the output voltage of the temperature detection sensor is detected and stored instep 18, and the detected output voltage of the temperature detection sensor is compared to a stored previous output voltage of the temperature detection sensor instep 19. Depending on the result of the comparison, the step 20 for detecting the output voltage of the temperature detection sensor may be repeated until the output voltage of the temperature detection sensor reaches to the set thaw reference point. And as the result of the comparison, when the output voltage of the temperature detection sensor has reached to the thaw reference point A, operation lapse time of the magnetron until the output voltage of the temperature detection sensor reaches to the thaw reference point A is detected and stored instep 21, and the additional operation time period of the magnetron is set based on the stored operation lapse time period of the magnetron until the thaw reference point A and the set cooking constant instep 22. The thaw reference point A is set on the output voltage of the temperature detection sensor corresponding to the food surface temperature of about 5 deg.C, which, according to experiments, corresponds to 1.67 V of the output voltage of the temperature detection sensor. Herein, the additional operation time period of the magnetron is obtained by multiplying the set cooking constant to the stored operation lapse time period up to the thaw reference point. Also, the step 23 for setting the additional operation time period of the magnetron for the cooking course without water boiling may be carried out by setting the additional operation time period of the magnetron based on the time period for the temperature detection sensor reaching to the thaw reference point and the set cooking constant. Herein, the additional operation time period of the magnetron is obtained by multiplying the set cooking constant to the operation lapse time period of the magnetron corresponding until the thaw reference point of the radiation heat of the cooking object. An additional magnetron operation time period setting step 24, 25, 26, 27, and 28 for the cooking course with water boiling is carried out for setting additional operation time period of the magnetron based on the time period for the output voltage of the temperature detection sensor to reach to a maximum rise point at taking the maximum rise point B of the output voltage of the temperature detection sensor as the reference detection point when the applied menu key is for a cooking course with water boiling, for example for scalding or smothering as the result of carrying out the cooking course identifying step. That is, the output voltage of the temperature detection sensor is detected and stored instep 24, and the detected output voltage of the temperature detection sensor is compared to a stored previous output voltage of the temperature detection sensor instep 25. Depending on the result of the comparison, the step 26 for detecting the output voltage of the temperature detection sensor may be repeated until the maximum rise point when the output voltage of the temperature detection sensor start to rise rapidly is to come. And as the result of the comparison, when the output voltage of the temperature detection sensor has reached to the maximum rise point B, operation lapse time of the magnetron until the output voltage of the temperature detection sensor reaches to the maximum rise point B is detected and stored instep 27, and the additional operation time period of the magnetron is set based on the stored operation lapse time period of the magnetron until the maximum rise point B and the set cooking constant instep 28. Herein, the additional operation time period of the magnetron is obtained by multiplying the set cooking constant to the stored operation lapse time period up to the maximum point. Also, the step for setting the additional operation time period of the magnetron for the cooking course with water boiling may be carried out by setting the additional operation time period of the magnetron based on the time period reaching to the maximum rise point at which the radiation heat of the cooking object starts to rise rapidly and the set cooking constant. Herein, the additional operation time period of the magnetron is obtained by multiplying the set cooking constant to the operation lapse time period of the magnetron corresponding to the maximum rise point of the radiation heat of the cooking object. After carrying out the additional magnetron operation time period setting step, a step for operating the magnetron 23 is carried out for operating the magnetron for the additional operation time period. As has been explained, this invention has advantages of, facilitating precise cooking control even with a menu requiring completion of cooking below water boiling point such as warming up and thawing because this invention allows setting of a reference detection point even below water boiling point with a temperature detection sensor, and, accordingly, economy because this invention does not require any additional sensors. Although the invention has been described in conjunction with specific embodiments, it is evident that many alternatives and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, the invention is intended to embrace all of the alternatives and variations that fall within the scope of the appended claims.

Claims: A method for automatic control of a microwave oven using stored (10) cooking constants (K), said cooking constants being related to kinds of cooking, comprising the steps of: determining (11) if a menu key has been applied, and if yes, then initializing (12) a cooking time period monitoring timer and storing (14) an initial value of the temperature detection sensor; setting (15) a cooking constant from the stored cooking constants in accordance with the applied menu key; operating (16) a magnetron and said cooking time period monitoring timer; identifying (17) the applied menu key as being a cooking course with no water boiling or a cooking course with water boiling; setting (18, 19, 20, 21, 22) an additional magnetron operation time period for a cooking course with no water boiling based on the elapsed time period (T1) at the time period when the output voltage of the temperature detection sensor reaches a predetermined thaw reference point (A), and the set cooking constant (K) when it is found that the selected menu key is for a cooking course with no water boiling; setting (24, 25, 26, 27, 28) an additional magnetron operation time period for a cooking course with water boiling based on the elapsed time period (T1) at the time period when the output voltage of the temperature detection sensor reaches a maximum rise point (B) and the set cooking constant (K) when it is found that the selected menu key is for a cooking course with water boiling; and operating (23) the magnetron for the set additional operation time period. The method for automatic control of a microwave oven as claimed in claim 1, characterized in that the additional magnetron operation time period setting step (18, 19, 20, 21, 22) for a cooking course without water boiling includes a step (18) for detecting and storing the output voltage of the temperature detection sensor, a step (19) for comparing the detected output voltage of the temperature detection sensor to a stored output voltage of the temperature detection sensor, a step (20) for repeating the step for detecting the output voltage of the temperature detection sensor until the output voltage of the temperature detection sensor reaches the thaw reference point (A) a step (21) for detecting and storing the operation lapse time (T1) of the magnetron, said lapse time being the time that has elapsed when the output voltage of the temperature detection sensor reaches the thaw reference point (A), when the output voltage of the temperature detection sensor has reached the thaw reference point (A), and a step (22) for setting the additional operation time period of the magnetron based on the stored operation lapse time period of the magnetron up to the thaw reference point (A) and on the set cooking constant (K). The method for automatic control of a microwave oven as claimed in claim 2, characterized in that said thaw reference point (A) is set on the output of the temperature detection sensor corresponding to 5°C of the food surface temperature. The method for automatic control of a microwave oven as claimed in claim 3, characterized in that said thaw reference point (A) is set on 1.67 V of the output of the temperature detection sensor. The method for automatic control of a microwave oven as claimed in claim 2, characterized in that said additional operation time period of the magnetron is obtained by multiplying the set cooking constant (K) with the stored operation lapse time period (T1) up to the thaw reference point (A). The method for automatic control of a microwave oven as claimed in claim 1, characterized in that the additional magnetron operation time period setting step (24, 25, 26, 27, 28) for a cooking course with water boiling includes a step (24) for detecting and storing the output voltage of the temperature detection sensor, a step (25) for comparing the detected output voltage of the temperature detection sensor to a stored output voltage of the temperature detection sensor, a step (26) for repeating the step for detecting the output voltage of the temperature detection sensor until the maximum rise point (B), at which the output voltage of the temperature detection sensor starts to rise rapidly, is reached, a step (27) for detecting and storing the operation lapse time (T1) of the magnetron, said lapse time (T1) being the time that has elapsed when the output voltage of the temperature detection sensor reaches to the maximum rise point, when the output voltage of the temperature detection sensor has reached to the maximum rise point (B), and a step (28) for setting the additional operation time period of the magnetron based on the stored operation lapse time (T1) of the magnetron up to the maximum rise point (B) and the set cooking constant (K). The method for automatic control of a microwave oven as claimed in claim 6, characterized in that the additional operation time period of the magnetron is obtained by multiplying the set cooking constant (K) with the stored operation lapse time period (T1). The method for automatic control of a microwave oven as claimed in claim 1, characterized in that the step (18, 19, 20, 21, 22) for setting the additional magnetron operation time period for a cooking course with no water boiling is carried out by setting the additional operation time period according to a thaw reference point (A) at which the radiation heat of the cooking object starts to rise and according to the set cooking constant (K). The method for automatic control of a microwave oven as claimed in claim 8, characterized in that the additional operation time period of the magnetron is set by multiplying the operation lapse time period (T1) up to the thaw reference point (A) where the rise of radiation heat of the cooking object starts, with the set cooking constant (K). The method for automatic control of a microwave oven as claimed in claim 1, characterized in that the step (24, 25, 26, 27, 28) for setting an additional magnetron operation time period for a cooking course with water boiling is carried out by setting the additional operation time period according to the maximum rise point (B) where the radiation heat of the cooking object reaches the maximum, and according to the set cooking constant (K). The method for automatic control of a microwave oven as claimed in claim 10, characterized in that the additional operation time period of the magnetron is set by multiplying the operation time period (T1) of the magnetron up to the maximum rise point (B) at which the rise of radiation heat of the cooking object reaches the maximum, with the set cooking constant (K).

Inventors: BU JONG UK, KIM TAE YUN, BU, JONG UK, KIM, TAE YUN
Applicants: LG ELECTRONICS INC, LG ELECTRONICS INC.
Application year: 1994
Main classification: H05B6
IPC codes: F24C7, H05B6